1. Field of the Invention
The present invention relates to an automatic optical inspection system and method, and particularly to an automatic optical inspection system and method using line scan cameras.
2. Description of the Related Art
The quality of sealing elements signifies whether the manufacturer has grasped the core technology and quality control capability. During inject-molding of sealing elements, the variation in pressure or temperature might bring about defects. However, the final quality control is still undertaken manually at present.
Thus, it can be seen in a modern production line that tens or even hundreds of workers should execute quality control tasks manually. In spite of so much manpower have been expended, it is still unlikely to detect all defective products. In the competitive environment nowadays, even a defective fraction of one thousandth is unacceptable. The quality control of sealing elements needs to perform small dimension measurements, shape comparisons and color recognitions fast and accurately. However, those tasks are hard to stably be executed with human eyes continuously. Further, tired human eyes could miss sometimes. Besides, the subjective judgment of each individual brings about the diversity of the quality control standard.
Sealing elements, such as packings, oil seals, and gaskets are devices to prevent rotating equipment such as pumps and compressors from leaking. They are usually made of rubber and PU (polyurethane). In the conventional manual inspection operation, high intensity light is used to illuminate sealing elements, and the optical refractions caused by a defect will reveal the defect itself. However, such an inspection method not only cause injuries to eyesights but also high in cost. In other words, experienced operators have to find and classify defects with naked eyes in the conventional inspection method. Tiredness and other factors will make even the most experienced inspectors fail to find defects sometimes. Besides, the inspection speeds of the inspectors are not always the same. Therefore, the conventional manual inspection method is expensive, unreliable and hard to meet the requirement of a modern production line.
The machine vision-based inspection technology is a promising solution to the problems of the conventional manual inspection method. A conventional technology proposed a scheme to capture and inspect the image of defects of the top and bottom surfaces of a sealing element. However, this technology does not provide the inspection of the inner and outer cylindrical surfaces of the sealing element, which are often the critical portions of a sealing element. A defect in the inner or outer cylindrical surfaces, such as a scratch or a blister, may make a hydraulic system or a reciprocating shaft system, which uses a lot of sealing elements, unable to operate. Moreover, the conventional technology cannot deal with the inspection of cylindrical surfaces because it utilizes an area-scan camera to capture the image of a curved surface. An area-scan camera acquires image of the curved surface not in a single shot but section by section in a plurality of shots. Such an approach is thus time-consuming. Besides, when a large-area curved surface is projected into a 2D plane, the image will be distorted. Although the conventional machine vision-based inspection technology is more accurate than the conventional manual inspection method, there is still room to improve.
Accordingly, the present invention provides an automatic optical inspection system and method to overcome the above-mentioned problems and promote the accuracy of defect inspection.